Radiant heater

ABSTRACT

A radiant heater is described which includes channel-shaped radiating elements mounted side-by-side in a housing. The channel-shaped elements are metal and give high strength with light weight. The channel-shaped elements have a high emittance surface backed by an air space for uniform distribution across the surface through convection and radiation and are also backed by insulation to reduce back side losses. In construction, each channel-shaped element is formed from nested U-shaped members having a resistance heater positioned therebetween and electrically insulated from the U-shaped members by layers of dielectric material. Electrical connections to the resistance extend from the ends of the elements and may be connected across a suitable source of electrical energy for operation.

United States Patent Desloge 1 RADIANT HEATER [72] Inventor: George B. Desloge, Frontenac, Mo.

[73] Assignee: Watlow Electric Manufacturing Company, St. Louis, Mo.

[22] Filed: Feb. 4, 1971 [21] Appl. No.: 112,743

[52] US. Cl ..219/354 [51] Int. Cl. ..H05b U019 [58] Field of Search ..2l9/339, 354, 552, 445, 553; 338/226, 306, 247

[56] References Cited UNITED STATES PATENTS 3,141,089 7/1964 Hultgreen ..219/354 X 1,067,869 7/1913 Falkenberg ..338/247 3,045,100 7/1962 Mills ..2l9/354 1,150,426 8/1915 l-ladaway ..2l9/544 51 Aug. 15, 1972 Primary Examiner-Bemard A. Gilheany Assistant Examiner-F. E. Bell Att0rneyGravely, Lieden 8L Woodruif ABSTRACT A radiant heater is described which includes channelshaped radiating elements mounted side-by-side in a housing. The channel-shaped elements are metal and give high strength with light weight. The channelshaped elements have a high emittance surface backed by an air space for uniform distribution across the surface through convection and radiation and are also backed by insulation to reduce back side losses. In construction, each channel-shaped element is formed from nested U-shaped members having a resistance heater positioned therebetween and electrically insulated from the U-shaped members by layers of dielectric material. Electrical connections to the resistance extend from the ends of the elements and may be connected across a suitable source of electrical energy for operation.

9 Claims, 8 Drawing figures PATENTEDAUG 15 I972 3. 684.859 sum 1 or 3 I i INVENTOR GEORGE B. DESLOGE WMMW ATTORN PATENTEDAus 15 I972 3.684.859

sumanrs FIG. 8 32 5% F6 um! [/6 INVENTOR GEORGE B. DESLOGE t MfWW ATTORNEY RADIANT HEATER BACKGROUND OF THE INVENTION This invention relates in general to electric heaters and more particularly to electric radiant heaters.

Present radiant heaters generally operate from high temperature sources of heat and distribute the heat by reflectors or by diffusion through a quartz, ceramic, or glass panel.

The glass or ceramic diffusers are not durable even though heavy and bulky.

It has been proposed to use flattened tubes backed with insulation over a surface as a heat distributor. These structures were weak structurally even though heavier than the nested channels of this invention. As there was no air space behind the strips, there was no even distribution of heat of temperature on the surface.

The radiant heaters of current manufacture which utilize reflectors behind their radiating elements do it to try to achieve effective distribution of the heat from the heating elements. These radiating elements should be positioned at the focal point of the reflector since any displacement from that point will scatter the infrared rays. Reflectors, furthermore, may increase the size and weight of such heaters significantly. Moreover, reflector-type radiant heaters of current manufacture operate with the heaters at relatively high temperatures and these temperatures are detrimental to the materials from which the heaters are made, resulting in short life in many instances. The high temperatures further necessitate the use of ceramic parts in many locations, but ceramic parts crack easily and therefore must be replaced.

Also, the radiating elements of most conventional radiant heaters are difficult to replace, and since those radiating elements have a limited life, many heaters are inoperative for extended periods for want of a repairman skilled enough to replace burned out radiating elements.

As conventional heaters have a high temperature source and wide radiating segments, it is hard to get a variety of width increments so that practically all radiant heaters of current manufacture are offered in a few limited sizes, and as a result in most instancesit is impossible to match a heater to the demand on it. Usually, a heater oversized in wattage or dimensions is employed and by reason of the oversize it cycles at relatively frequent intervals. This cycling in turn decreases the life of the heater.

SUMMARY OF THE INVENTION A principal object of the present invention is to provide a uniform source of heat without glass, ceramic, or reflectors which has a high energy output with a low temperature source. Another principal object of the present invention is to provide a radiant heater which is compact in size and light in weight. Another object is to produce a radiant heater which effectively distributes heat without a reflector. A further object is to provide a radiant heater which is rugged in construction because it has no glass or ceramic parts. Another object is to provide a radiant heater which operates at a relatively low temperature so as to extend the life of the materials from which it is constructed, and to give greater efficiency because more materials are receptive to the radiant energy from a low temperature source. An additional object is to provide a radiant heater which has radiating elements which are easily replaced. Still another object is to provide a radiant heater which may be made in a variety of sizes from standard parts without a significant increase in production costs, thereby enabling heaters to be matched with the demand so as to avoid cycling of the heaters. Yet another object is to provide a heater which radiates from substantially one entire surface. An additional object is to provide a heater which is easily installed on supporting structures. These and other objects and advantages will become apparent hereinafter.

The present invention is embodied in a radiant heater including a housing having a plurality of channel-shaped radiating elements contained therein in side-by-side relation. The elements have a very high emittance surface, the backside of which is spaced from an insulation wall to reduce heat losses and provide even distribution of heat across the radiating surface. The invention also resides in the individual radiating elements and in the parts and in the arrangements and combinations of parts hereinafter described and claimed.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form part of the specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a perspective view of a radiant heater constructed in accordance with and embodying the present invention,

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1; I

FIGS. 3 and 4 are sectional views taken along lines 33 and 44, respectively, of FIG. 2;

FIG. 5 is a transverse sectional view of a radiating bar which forms part of the present invention;

FIG. 6 is a fragmentary longitudinal sectional view of the radiating bar;

FIG. 7 is an exploded perspective view of the radiating bar; and

FIG. 8 is a fragmentary elevational view, partially broken away and in section, of the end of a radiant heater provided with electrical terminals in its end cap.

DETAILED DESCRIPTION Referring now to the drawings, 2 designates a radiant heater which basically includes a housing 4 (FIG. 1) a plurality of radiating bars 6 located side-by-side in the housing 4, and an insulating material 8 (FIGS. 24) contained within the housing 4 behind the radiating bars 6.

The housing 4 includes a channel-shaped containing member 10 (FIGS. 2-4) preferably formed from stainless steel and consisting of a base wall 12 and a pair of side walls 14 formed integral with and presented perpendicularly with respect to the base wall 12. Outwardly from the base wall 12, the sidewalls 14 are doubled back upon themselves and into the interior of the containing member 10 to form a longitudinally extending interior lip 16 (FIGS. 3 and 4) and a curved outer edge 18. The sidewalls 14 are reinforced by end cross members 20 (FIGS. 2 and 3) which extend between those walls 14 slightly inwardly from their ends. The cross members 20 are located against the inner edges of the lips 16, that is to say they extend across the housing 4 at the inwardly presented edges of the lips 16. In one form of the invention illustrated in detail in FIGS. 2 and 4, the mid-portions of the walls 14 are connected by another or center cross member 22 including an outwardly bowed portion 24 having slots 26 extending transversely through it, but not through the continuous lateral portions on each side of that bowed portion 24.

The bowed portion 24 projects outwardly almost to the curved edge 18 and its ends are spaced slightly inwardly from the lips 16, which are in turn spaced inwardly from the sidewalls 14. The center cross member is attached to the walls by upturned ends 28.

In an alternate form of the invention (not specifically illustrated) the center member has the same configuration as the end members 20. In this form, the radiating bars 6 rest on and are supported by the three cross members 20.

The ends of the containing member 10 are closed by end caps 30 which also form part of the housing 4 and are likewise preferably formed from stainless steel. Each end cap 30 includes an end wall 32 (FIG. 2) which is backed on its interior face by a layer of high temperature dielectric material 33 such as mica and is connected to the base wall 12 by a hinge 3 4 so that the end cap 30 can be folded outwardly away form its closure forming position at the end of the containing member (FIG. 8). This affords access to the interior of the containing member 10. If desired, the ends can be removably fastened by screws, detents, or other suitable means. Each end cap 30 also includes a pair of side flanges 36 (FIGS. 1 and 3) which are formed integral with the end wall 32 and overlie the sidewalls 14 when the end wall 32 is folded against the ends of the sidewalls 14. In addition, each end cap 30 includes a cross flange 38 (FIGS. 1 and 2) which is also formed integral with the end wall 32 and extends between the ends of the side flanges 36 so as to overlie the curved edges 18 on the sidewalls 14 of the containing member 10. The end caps 30 are maintained in their closure forming positions at the ends of the containing member 10 by the screws 40 which extend through the side flanges 36 and thread into the sidewalls 14. The end walls 32 and side flanges 36 on each end cap 30 furthermore extend beyond the hinge 34 so as to form mounting legs 42 for supporting the heater 2 from a suitable supporting structure (not shown).

The base wall 12 is fitted with a pair of threaded electrical terminals 44 (FIG. 2) which are electrically isolated therefrom and connect with longitudinally extending bus bars 46 on the inwardly presented side of the wall 12. One bus bar 46 extends longitudinally to one end of the containing member 10 while the other bus bar 46 extends in opposite direction to the other end of the containing member 10. The bus bars 46 are also formed from stainless steel and turn away from the base wall 12 at the ends of that wall 10 in the provision of connecting tabs 48 which are spaced inwardly from the end walls 32 of the end caps 30. Each bus bar 46 is separated from the base wall 12 by a thin sheet of high temperature dielectric material 50.

The insulating block 8 can withstand high temperature and further does not conduct electricity. For all practical purposes, it fills that portion of the housing 4 located between the base wall 12 on one hand and the cross members 20 and 22 on the other. PV" Supertemp Block which is marketed by Eagle-Picher is suitable for the insulating block 8.

The radiating bars 6 fit into the portion of the housing 4 not occupied by the insulating pad 8, that is the portion located outwardly beyond the cross members 20 and 22, and they are disposed between the interior lips 16 on the side walls 14. The bars 6 are positioned against the cross members 20 and 22 (FIGS. 2-4) and are further positioned side-by-side between the lips 16 which prevent the bars 6 from shifting laterally in the housing 4. The end walls 32 on the end caps 30, on the other hand, obscure the ends of the bars 6, while the cross flanges 38 on the end caps 30 overlie the outwardly presented surfaces on the bars 6.

Each radiating bar 6 has U- or channel-shaped configuration (FIG. 5), possessing a pair of spaced side flanges 56 and a connecting bight or base portion 50 extending between the flanges 56. The outwardly presented surface of the bight portion 58 is treated to produce a surface of high emissivity. This can be done in a number of ways, such as coating with a high temperature paint, flame sprayed coatings, sand blasting, etc. The spacing between the inwardly presented surfaces of the opposed flanges 56 is slightly greater than the spacing between the closest margins of adjacent slots 26 in the bowed portion 24 of the center cross member 22 (FIG. 4). In other words, the length of each bowed segment of the bowed portion 24 is slightly less than the spacing between the flanges 26. Moreover, the width of each slot 26 is slightly greater than twice the thickness of a flange 56. If the flat center cross member is used, this is not relevant, of course.

The radiating bars 6 fit into the housing 4 with the flanges 56 projecting inwardly toward the insulating block 8 and the emissive surfaces of the bight portions 58 presented outwardly (FIGS. 3 and 4). As previously noted the bars 6 are positioned side-by-side, and when so disposed the side flanges 56 on adjacent bars facewise abut each other. These abutting side flanges furthermore fit into the slots 26 of the bowed portion 24 on the center cross member 22. The outermost side flanges 56 on the two outer bars 6, of course, do not abut against any other flanges 56, but instead abut against the interior lips 16 formed on the side walls 14 of the containing member 10. These outermost flanges 56 furthermore fit into the spaces between the ends of the bowed portion 24 and the interior lips 16 of the side walls 14.

The side flanges on the radiating bars 6 are provided with aligned apertures 60 (FIGS. 4) which open into the trough or interior of the bowed portion 24 on the center cross member 22, and likewise the side walls 14 and interior lips 16 are also provided with apertures 62 which align with the bowed portion 24 as well as with the apertures 60. Fitted through the apertures 62 and 60 as well as through the interior of the bowed portion 24 aligned with those apertures is a restraining pin 64 which prevents the radiating bars 6 from bowing outwardly or sliding longitudinally as their temperature rises.

The pin 64 holds the assembly together while still allowing for longitudinal expansion of the channelshaped radiating bars 6.

If the flat center cross member is used with the restraining pin 64, the pin 64 fits through the openings 62 in the side walls 14, 16 and the openings 60 in the radiating bars 6. There is no connection to the cross member in this form of the invention.

In certain types of construction it is possible to eliminate the center pin and utilize the end caps as a retaining means for the radiating bars.

Each radiating bar 6 comprises (FIGS. 5-7) an outer channel-shaped member 70 and an inner channelshaped member 72, both of which are formed from stainless steel and have the same general configuration as the bar 6 itself, that is to say they both have a pair of side flanges connected by a bight or base portion. The inner channel-shaped member 72 is slightly smaller than the outer member 70, and fits or nests within the outer member 70. Furthermore, the inner member 72 is somewhat shorter than the outer member 70 so that the outer member 70 projects beyond both ends of the inner member 72. The side flanges of the two members 70 and 72 may be spot welded or otherwise joined together to create a unitary channel-shaped structure.

Fitted between the bight or connecting portions of the two channel-shaped members 70 and 72 are two thin strips 74 nd 76 of sheet-like dielectric material which is capable of withstanding high temperatures. Mica insulating strips are ideally suited for this purpose. In lieu of the separable dielectric strips 74 and 76 a spray deposit such as aluminum oxide or an insulating cement such as those made by Savereisen may be used. The dielectric strip 74 extends the full length of the outer channel-shaped member 70, against which it lies, whereas the strip 76 is slightly longer than the inner channel member 72 against which it lies but is still shorter than the outer channel-like member 70 and its dielectric strip 72.

The dielectric strips 74 and 76 have a resistance-type electrical heating element 78 fitted between them, and that element 78 preferably is a sinuated wire. Other types of elements such as sprayed coatings, notched ribbons, etc. may be used. The strips 74 and 76, of course, electrically isolate the element 78 from the channel-shaped members 70 and 72 so that the exposed surfaces of the bar 6 remain at ground potential. Each end of the sinuated wire element 18 is connected to a flexible connector tab 80 which projects beyond the ends of the dielectric strips 74 and 76 and is bent in the direction of the side flanges 56. Thus, the connector tabs 80 are disposed between the side flanges 56 and project away from the bight portion 58 of the bar 6.

The connector tabs 80 are connected to the connecting tabs 48 on the bus bars 46 or to the connecting tabs 80 in adjacent radiating bars 6, depending on the type of connection which is desired. Likewise, the heater 2 may be wired for three phase electrical power by incorporating another threaded terminal 44 and bus bar 46 into the housing 4.

When the threaded terminals 44 are placed across a suitable source of electrical energy, current is conducted through the bus bars 46, connecting tabs 80, and sinuated wire elements 78. This causes the temperature of the wire elements 78 to rise and this in turn elevates the temperature of the radiating bars 6. The electrical energy supplied to the heater 2 at the threaded terminals 44 should be sufficient to raise the temperature of the bars 6 to a range of approximately 600 F. to about l,400 F. Consequently, the bars 6 radiate heat from their exposed surfaces. Since the exposed surfaces are highly emissive, the emissivity of the unit approaches that of a theoretical black body, making the heater 2 extremely efficient.

The insulating block 8 keeps the base wall 12 of the housing 4 relatively cool.

The space 22 between the insulating block 8 and the backside of the bars 6 serves to evenly distribute the heat and prevent one part of the emissive surface from building up to a high temperature. Thus, the entire emissive surface is usable and evenly radiates heat.

The rearward extension of the mounting legs 42 positions the hottest part of the heater 2 away from the supporting structure. In some installations the legs 42 are not necessary.

Should the sinuated wire heating element 78 in one of the heater bars 6 break, the adjacent bars 6 will conduct heat to the defective bar 6 so that its exposed surface will continue to radiate, provided of course that the bars 6 are wired in parallel or some other way which does not disrupt the circuit through the remaining bars 6.

In this connection, a defective radiating bar 6 is quickly and easily replaced merely by removing the screws 40 and swinging the end caps 30 away from the containing member 10 (FIG. 8) so as to expose the ends of the bars 6. The connecting tabs 80 on the defective bar are then disconnected from the connecting tabs 80 on adjacent bars 6 or the connecting tabs 48 on the bus bars 46, whatever the case may be. Finally, the restraining pin 64 is withdrawn from the apertures 60 in the side flanges 56 of the defective bar 6, and the defective bar 6 is removed. Anew radiating bar 6 is thereafter installed by utilizing the reverse of the foregoing procedure.

The exposed surfaces of the radiating bars 6 occupy almost one entire side or face of the radiant heater 6 (FIG. 1). Indeed, only the cross flanges 38 on the end caps 30 and the curved edges 18 on the side walls 14 do not serve as effective radiating surfaces, but these surfaces are extremely small in comparison to the exposed surfaces of the bars 6. By reason of this fact, the radiant heater 2 is extremely compact. In this connection, it should be noted that the heater 2 does not possess any reflector as do conventional radiant heaters, and accordingly considerable space is saved.

Aside from being highly compact, the radiant heater 2 is also light in weight and extremely rugged in construction. As to the latter feature, most of the components are formed from stainless steel so that oxida' tion of the metal does not occur even at high temperatures. Moreover, no ceramic parts are used and therefore the cracking problem associated with ceramic materials does not exist.

Finally, it is not necessary to elevate the temperature of the bars to extremely high values in order to achieve effective radiation as is true of the heating elements in conventional reflectortype heaters. It is preferred to operate the radiating bars 6 in the range of about 600 F. to about l,5()0 F. which creates wave lengths capable of being absorbed by most substances, irrespective of color or opacity. The lower operating temperatures coupled with the extremely durable materials enable the heater 2 to operate for extremely long periods of time, even when cycled.

From a production and marketing standpoint the radiating bars 6 may be provided in standard lengths, and housings 4 may be provided to accommodate the standard lengths in various numbers. For example, one housing may hold three -inch bars, while another housing may hold six 15-inch bars. Thus, it is possible to provide a great variety of heaters or to even design custom heaters for different applications, all without incurring a significant increase in production costs.

It is possible to install the threaded terminals 44 in the end caps 30 (FIG. 8), in which case flexible metal connecting strips 82 should connect the terminals 44 with the bus bars 46 or connecting tabs 80 in the radiating bars 6, depending on the type of connection which is desired. The connecting strips 82 should furthermore contain several accordion-like creases 84'so that the strip 82 will extend when the end cup 30 is swung outwardly on the hinge 32 and will contract when the end cap 30 is closed.

The terminals also can be mounted through the sides 28 if desired. In fact the mounting of the terminals is relatively unrestricted except for the radiating surface.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

l. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar being generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, a heat insulating material positioned in the housing between the radiating bars and the base wall, an air space between the inner side of the radiating bars and the insulating material, and cross members between the sidewalls of the housing supporting the radiating bars, one of the cross members being positioned near the center of the housing and having an outwardly bowed portion extending across the housing transverse to the bars, the outwardly bowed portion having slots into which inturned flanges on the radiating bars fit, the flanges being apertured behind the outwardly bowed portion; and including a restraining pin extending behind the outwardly bowed portion and through the apertures in the bar flange whereby the bars cannot be withdrawn from the housing when the restraining pin is in place, and the ends of the bars are free to expand.

2. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar being generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, the sidewalls of the housing and the flanges on the channel-shaped radiating bars being provided with aligned apertures near the centers thereof, a removable pin means positioned through the apertures to restrain the bars in the housing, a heat insulating material positioned in the housing between the radiating bars and the base wall, and an air space between the inner side of the radiating bars and the insulating material.

3. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar being generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element ex tending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, cross members between the sidewalls of the housing supporting the radiating bars, a heat insulating material positioned in the housing between the radiating bars and the base wall, an air space between the inner side of the radiating bars and the insulating material, the housing having end caps at the ends of the base and sidewalls, said end caps extending over the ends of the radiating bars to cover the terminals and retain the bars in the housing, said end caps being movable away from the ends of the bars so that the bars can be withdrawn from the containing member.

4. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, a cross member between the sidewalls of the housing supporting the radiating bars, a heat insulating material positioned in the housing between the radiating bars and the base wall, an air space between the inner side of the radiating bars and the insulating material, housing end caps at the ends of the base and sidewalls of the housing, said end caps extending over the ends of the radiating bars to cover the terminals and retain the bars in the housing, each end cap comprising side flanges which extend along the sidewalls, and means for detachably securing the side flanges of the end cap to the sidewalls of the containing member.

5. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a radiating bar mounted lengthwise in the housing between the sidewalls and exposed outwardly through the open side thereof, the bar having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surface of the bar being exposed outwardly from the open side of the housing, means for retaining the bar in the housing, a heat insulating material positioned in the housing between the radiatof the housing, said end cap extending over the end of the radiating bar and being movable away from the end of the bar so that the bar can be withdrawn from the housing, and means for locking the end cap to the housmg.

6. A radiant heater according to claim 5 wherein an air space is provided between the inner side of the radiating bars and the insulating material.

7. A radiant heater according to claim 5 wherein legs extend beyond the base wall of the housing for mounting the heater.

8. A radiant heater according to claim 3 wherein the end cap is hinged to the base wall.

9. A radiant heater according to claim 3 wherein the end cap has projections beyond the base wall of the containing member to form mounting legs for mounting the heater on a supporting structure. 

1. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar being generally channelshaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, a heat insulating material positioned in the housing between the radiating bars and the base wall, an air space between the inner side of the radiating bars and the insulating material, and cross members between the sidewalls of the housing supporting the radiating bars, one of the cross members being positioned near the center of the housing and having an outwardly bowed portion extending across the housing transverse to the bars, the outwardly bowed portion having slots into which inturned flanges on the radiating bars fit, the flanges being apertured behind the outwardly bowed portion; and includinG a restraining pin extending behind the outwardly bowed portion and through the apertures in the bar flange whereby the bars cannot be withdrawn from the housing when the restraining pin is in place, and the ends of the bars are free to expand.
 2. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar being generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, the sidewalls of the housing and the flanges on the channel-shaped radiating bars being provided with aligned apertures near the centers thereof, a removable pin means positioned through the apertures to restrain the bars in the housing, a heat insulating material positioned in the housing between the radiating bars and the base wall, and an air space between the inner side of the radiating bars and the insulating material.
 3. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar being generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, cross members between the sidewalls of the housing supporting the radiating bars, a heat insulating material positioned in the housing between the radiating bars and the base wall, an air space between the inner side of the radiating bars and the insulating material, the housing having end caps at the ends of the base and sidewalls, said end caps extending over the ends of the radiating bars to cover the terminals and retain the bars in the housing, said end caps being movable away from the ends of the bars so that the bars can be withdrawn from the containing member.
 4. A radiant heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a plurality of radiating bars mounted side-by-side in the housing between the sidewalls and exposed outwardly through the open side thereof, each bar generally channel-shaped and having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surfaces of the bars being exposed outwardly from the open side of the housing, a cross member between the sidewalls of the housing supporting the radiating bars, a heat insulating material positioned in the housing between the radiating bars and the base wall, an air space between the inner side of the radiating bars and the insulating material, housing end caps at the ends of the base and sidewalls of the housing, said end caps extending over the ends of the radiating bars to cover the terminals and retain the bars in the housing, each end cap comprising side flanges which extend along the sidewalls, and means for detachably securing the side flanges of the end cap to the sidewalls of the containing member.
 5. A radiaNt heater comprising a housing having an open side, sidewalls, and a base wall connected to and extending between the sidewalls, the open side of the housing being located opposite to the base wall; a radiating bar mounted lengthwise in the housing between the sidewalls and exposed outwardly through the open side thereof, the bar having a high emittance outer surface portion and a resistance-type heating element extending along the inner side of the high emittance portion, and electrical insulation means between the element and the inner side of the bar, the high emittance surface of the bar being exposed outwardly from the open side of the housing, means for retaining the bar in the housing, a heat insulating material positioned in the housing between the radiating bar and the base wall, a movable end cap at one end of the housing, said end cap extending over the end of the radiating bar and being movable away from the end of the bar so that the bar can be withdrawn from the housing, and means for locking the end cap to the housing.
 6. A radiant heater according to claim 5 wherein an air space is provided between the inner side of the radiating bars and the insulating material.
 7. A radiant heater according to claim 5 wherein legs extend beyond the base wall of the housing for mounting the heater.
 8. A radiant heater according to claim 3 wherein the end cap is hinged to the base wall.
 9. A radiant heater according to claim 3 wherein the end cap has projections beyond the base wall of the containing member to form mounting legs for mounting the heater on a supporting structure. 